@setfilename standards.info
@settitle GNU Coding Standards
@c This date is automagically updated when you save this file:
-@set lastupdate December 10, 2011
+@set lastupdate December 31, 2011
@c %**end of header
@dircategory GNU organization
* System Functions:: Portability and ``standard'' library functions.
* Internationalization:: Techniques for internationalization.
* Character Set:: Use ASCII by default.
-* Quote Characters:: Use `...' in the C locale.
+* Quote Characters:: Use "..." or '...' in the C locale.
* Mmap:: How you can safely use @code{mmap}.
@end menu
around each string that might need translation---like this:
@example
-printf (gettext ("Processing file `%s'..."));
+printf (gettext ("Processing file '%s'..."), file);
@end example
@noindent
This permits GNU gettext to replace the string @code{"Processing file
-`%s'..."} with a translated version.
+'%s'..."} with a translated version.
Once a program uses gettext, please make a point of writing calls to
@code{gettext} when you add new strings that call for translation.
@cindex quote characters
@cindex locale-specific quote characters
@cindex left quote
+@cindex right quote
+@cindex opening quote
+@cindex single quote
+@cindex double quote
@cindex grave accent
+@set txicodequoteundirected
+@set txicodequotebacktick
-In the C locale, GNU programs should stick to plain ASCII for quotation
-characters in messages to users: preferably 0x60 (@samp{`}) for left
-quotes and 0x27 (@samp{'}) for right quotes. It is ok, but not
-required, to use locale-specific quotes in other locales.
+In the C locale, the output of GNU programs should stick to plain
+ASCII for quotation characters in messages to users: preferably 0x22
+(@samp{"}) or 0x27 (@samp{'}) for both opening and closing quotes.
+Although GNU programs traditionally used 0x60 (@samp{`}) for opening
+and 0x27 (@samp{'}) for closing quotes, nowadays quotes @samp{`like
+this'} are typically rendered asymmetrically, so quoting @samp{"like
+this"} or @samp{'like this'} typically looks better.
-The @uref{http://www.gnu.org/software/gnulib/, Gnulib} @code{quote} and
-@code{quotearg} modules provide a reasonably straightforward way to
-support locale-specific quote characters, as well as taking care of
-other issues, such as quoting a filename that itself contains a quote
-character. See the Gnulib documentation for usage details.
+It is ok, but not required, for GNU programs to generate
+locale-specific quotes in non-C locales. For example:
-In any case, the documentation for your program should clearly specify
-how it does quoting, if different than the preferred method of @samp{`}
-and @samp{'}. This is especially important if the output of your
-program is ever likely to be parsed by another program.
+@example
+printf (gettext ("Processing file '%s'..."), file);
+@end example
+
+@noindent
+Here, a French translation might cause @code{gettext} to return the
+string @code{"Traitement de fichier
+@guilsinglleft{}@tie{}%s@tie{}@guilsinglright{}..."}, yielding quotes
+more appropriate for a French locale.
-Quotation characters are a difficult area in the computing world at
-this time: there are no true left or right quote characters in Latin1;
-the @samp{`} character we use was standardized there as a grave
-accent. Moreover, Latin1 is still not universally usable.
+Sometimes a program may need to use opening and closing quotes
+directly. By convention, @code{gettext} translates the string
+@samp{"`"} to the opening quote and the string @samp{"'"} to the
+closing quote, and a program can use these translations. Generally,
+though, it is better to translate quote characters in the context of
+longer strings.
-Unicode contains the unambiguous quote characters required. However,
-Unicode and UTF-8 are not universally well-supported, either.
+If the output of your program is ever likely to be parsed by another
+program, it is good to provide an option that makes this parsing
+reliable. For example, you could escape special characters using
+conventions from the C language or the Bourne shell. See for example
+the option @option{--quoting-style} of GNU @code{ls}.
-This may change over the next few years, and then we will revisit
-this.
+@clear txicodequoteundirected
+@clear txicodequotebacktick
@node Mmap
@example
* keyboard.c (menu_bar_items, tool_bar_items)
-(Fexecute_extended_command): Deal with `keymap' property.
+(Fexecute_extended_command): Deal with 'keymap' property.
@end example
When you install someone else's changes, put the contributor's name in
@cindex conditional changes, and change logs
@cindex change logs, conditional changes
-C programs often contain compile-time @code{#if} conditionals. Many
-changes are conditional; sometimes you add a new definition which is
-entirely contained in a conditional. It is very useful to indicate in
-the change log the conditions for which the change applies.
+Source files can often contain code that is conditional to build-time
+or static conditions. For example, C programs can contain
+compile-time @code{#if} conditionals; programs implemented in
+interpreted languages can contain module imports of function
+definitions that are only performed for certain versions of the
+interpreter; and Automake @file{Makefile.am} files can contain
+variable definitions or target declarations that are only to be
+considered if a configure-time Automake conditional is true.
+
+Many changes are conditional as well: sometimes you add a new variable,
+or function, or even a new program or library, which is entirely
+dependent on a build-time condition. It is useful to indicate
+in the change log the conditions for which a change applies.
-Our convention for indicating conditional changes is to use square
-brackets around the name of the condition.
+Our convention for indicating conditional changes is to use
+@emph{square brackets around the name of the condition}.
-Here is a simple example, describing a change which is conditional but
-does not have a function or entity name associated with it:
+Conditional changes can happen in numerous scenarios and with many
+variations, so here are some examples to help clarify. This first
+example describes changes in C, Perl, and Python files which are
+conditional but do not have an associated function or entity name:
@example
-* xterm.c [SOLARIS2]: Include string.h.
+* xterm.c [SOLARIS2]: Include <string.h>.
+* FilePath.pm [$^O eq 'VMS']: Import the VMS::Feature module.
+* framework.py [sys.version_info < (2, 6)]: Make "with" statement
+ available by importing it from __future__,
+ to support also python 2.5.
@end example
-Here is an entry describing a new definition which is entirely
-conditional. This new definition for the macro @code{FRAME_WINDOW_P} is
-used only when @code{HAVE_X_WINDOWS} is defined:
+Our other examples will for simplicity be limited to C, as the minor
+changes necessary to adapt them to other languages should be
+self-evident.
+
+Next, here is an entry describing a new definition which is entirely
+conditional: the C macro @code{FRAME_WINDOW_P} is defined (and used)
+only when the macro @code{HAVE_X_WINDOWS} is defined:
@example
* frame.h [HAVE_X_WINDOWS] (FRAME_WINDOW_P): Macro defined.
@end example
-Here is an entry for a change within the function @code{init_display},
-whose definition as a whole is unconditional, but the changes themselves
-are contained in a @samp{#ifdef HAVE_LIBNCURSES} conditional:
+Next, an entry for a change within the function @code{init_display},
+whose definition as a whole is unconditional, but the changes
+themselves are contained in a @samp{#ifdef HAVE_LIBNCURSES}
+conditional:
@example
* dispnew.c (init_display) [HAVE_LIBNCURSES]: If X, call tgetent.
@end example
-Here is an entry for a change that takes affect only when
+Finally, here is an entry for a change that takes effect only when
a certain macro is @emph{not} defined:
@example
projects / gnulib.git / blobdiff